The human nervous system includes the brain and the spinal cord, collectively known as the central nervous system. The central nervous system includes nerve fibers that transmit nerve signals to, from, and within the brain and spinal cord. The network of nerves in the remaining portions of the human body forms the peripheral nervous system. A system of peripheral nerves connects directly to the brain to control various brain functions, such as vision, eye movement, hearing, facial movement, and feeling. Another system of peripheral nerves, known as the autonomic nervous system, controls autonomic functions. Autonomic functions include blood pressure, body temperature, heartbeat, blood vessel diameter control, intestinal movements, actions of many internal organs, and other body activities and functions that occur without voluntary control.
Neurological disorders may affect the human nervous system. Some neurological disorders (e.g., epilepsy and depression) may be monitored, treated with medication, with neurostimulation, or a combination thereof. Neurostimulation may include electrical stimulation of the nervous system. Forms of neurostimulation may include cranial nerve stimulation, such as vagus nerve stimulation (VNS) or trigeminal nerve stimulation (TNS). A device that applies TNS may be configured to apply subcutaneous TNS, transcutaneous TNS, or both. VNS and subcutaneous TNS may require surgical implantation of electrodes in a patient. Transcutaneous TNS may be implemented by external electrodes coupled to the patient in one or more regions where nerve branches are near the surface of the skin.